This invention relates to a fluid displacement apparatus, and more particularly, to an improvement in a rotation preventing/thrust bearing device for an orbiting member fluid displacement apparatus.
There are several types of fluid displacement apparatus which utilize an orbiting piston or fluid displacing member, such as a scroll, driven by a Scotch yoke type shaft coupled to an end surface of the piston or displacing member. One such apparatus, disclosed in U.S. Pat. No. 1,906,142 to John Ekelof, is a rotary machine which has an annular eccentrically movable piston adapted to act within an annular cylinder. The annular cylinder has a radial transverse wall. One end of the wall of the cylinder is fixedly mounted. Another wall is formed as a cover disc connected to the annular piston, and is driven by a crank shaft. Other prior art apparatus of this type are shown in U.S. Pat. Nos. 801,182 and 3,500,119. Though the present invention applies to either type of fluid apparatus, i.e., using either an annular piston or a scroll-type piston, the description will be limited to a scroll type compressor. The term piston is used generically to describe a movable member of any suitable configuration within fluid displacement apparatus.
U.S. Pat. No. 801,182 (Creux) discloses a device including two scroll members each having a circular end plate and a spiroidal or involute spiral element. These scroll members are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scroll members shifts the line contacts along the spiral curved surfaces and, as a result, the volume of the fluid pockets changes. Since the volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion, the scroll type fluid displacement apparatus is applicable to compress, expand or pump fluids.
Generally, in the conventional scroll type fluid displacement apparatus, one of the scroll members is fixed to a housing and the other scroll member, which is the orbiting scroll member, is eccentrically supported on a crank pin of a rotating shaft to cause orbital motion. The scroll type apparatus also includes a rotation preventing device which prevents rotation of the orbiting scroll member to thereby maintain the scroll members in a predetermined angular relationship during operation of the apparatus.
Sealing along the line contacts of the above conventional scroll type apparatus must be maintained because the fluid pockets are defined by the line contacts between the two spiral elements. As the line contacts shift along the surface of the spiral elements due to the optical motion of the orbiting scroll member, the volume of the fluid pockets changes.
Since the orbiting scroll member in conventional scroll type apparatus is supported on a crank pin in a cantilever manner, an axial slant of this orbiting scroll member occurs. Axial slant also occurs because the movement of the orbiting scroll member is not rotary motion around the center of the scroll member, but is orbiting motion caused by the eccentric movement of a crank pin driven by the rotation of the drive shaft. Several problems result from the occurrence of this axial slant including improper sealing of the line contacts, vibration of the apparatus during operation and noise caused by physical striking of the spiral elements. One simple and direct solution to this problem is the use of a thrust bearing device for carrying the axial loads. Thus, scroll type fluid displacement apparatus is usually provided with a thrust bearing device within the housing.
One recent attempt to improve the rotation preventing and thrust bearing devices in scroll type fluid displacement apparatus is described in U.S. Pat. Nos. 4,160,629 (Hidden et al) and 4,259,043 (Hidden et al). The rotation preventing and thrust bearing devices in these U.S. patents are integral with one another. The rotation preventing/thrust bearing device described in these U.S. patents (see, e.g., FIG. 7 of Hidden et al Pat. No. 4,259,043) comprises one set of indentations formed on the end surface of the circular plate of the orbiting scroll member and a second set of indentations formed on the end surface of a fixed plate attached to the housing. A plurality of balls or spheres are placed between the indentations of both surfaces. All the indentations have the same cross-sectional configuration and the center of all the indentations formed on both end surfaces are located on circles having the same radius. As a result, the machining and fabrication of these indentations to accurate dimensions is very difficult and intricate.
To avoid these latter disadvantages, an improvement of the rotation preventing/thrust bearing device is described in copending application Ser. No. 356,647 entitled "Orbiting Member Fluid Displacement Apparatus With Rotation Preventing Mechanism," which was filed on the same date as this application by Takayuki Iimori, Kiyoshi Terauchi and Seiichi Sakamoto and which is assigned to the same assignee. This application discloses a rotation preventing/thrust bearing device comprising a fixed portion, an orbit portion and a plurality of balls or spheres. The fixed portion includes a fixed race and ring and the orbit portion includes an orbit race and ring. The fixed and orbit rings have a plurality of holes or pockets; the holes on the fixed ring correspond to the holes on the orbit ring. The races are formed separately from the rings, and then they are fastened to surfaces of the housing and the orbiting scroll by fastening devices. Since the races and rings are discrete parts, the holes or pockets formed on the rings are formed by a press working process.
A large number of the pockets are formed in the rings of the above device because the rotation preventing/thrust bearing device not only prevents rotation of the orbiting scroll, and maintains the angular relationship between the scrolls, but it also supports the axial load. In view of this large number of pockets formed on the rings, and the criticality of the distance between the adjacent pockets as contrasted to the thickness of the ring, several press working processes or steps are necessary to form the pockets. However, in the press working processes, dimensional errors of pitch and size are unavoidable. Since these dimensional errors will be compounded between the rings, such dimensional errors will adversely affect the actual orbiting locus permitted by the mechanism and other operations and performance of the scroll type fluid displacement apparatus.